The present invention relates to a new and improved apparatus for tensioning the warp thread sheet or set of warp threads of a weaving machine, in particular the warp pile of a Terry weaving machine or loom, containing a deflection beam yielding to the alternating tensions of warp threads which are withdrawn from a warp beam.
It is generally known that particularly with Terry weaving machines the inertia of the moving parts of the apparatus for tensioning the pile warp are of great importance, because of the great number of movements during the nep formation and the moderate forces which have to be applied for producing the slight warp pile tension. In particular, considerable variations of the pile warp tension can be observed. Moreover, during a full stroke of the reed for forming the pile neps the pile warp threads experience a sudden acceleration, which is transmitted to the moving parts of the tensioning apparatus which are under the effect of forces producing the tension of the pile warp. The force for accelerating such moving parts is thus dependent on the inertia masses and has to be supplied by the pile warp which thus undergoes a corresponding increase in tension. Therefore, it may happen that some pile warp threads, which are still loosely bound only by a few weft threads, initially do not follow the reed, whereby some thread length for the nep formation gets lost. Furthermore, the moveable parts of the tensioning apparatus for the pile warp depart from their rest position and swing out when the reed beats the woven cloth. When they return to their rest position under the effect of the force creating the pile warp tension, such movable parts are stopped by the pile warp, which thus experiences another increase in tension. Such increase may, in turn, consume thread length from the neps causing these to become irregular.
In order to reduce the inertia mass of the movable parts at the tensioning apparatus for the pile warp, there has been proposed in German Pat. No. 2,162,396 using a deflection beam for warp thread sheets, wherein a rigid support element, which is mounted at its ends upon the machine carriage and extends over the width of the warp thread sheet, is at least partially surrounded by a thereto attached deflection element which is formed of a substantially blade-like material and elastically yields to the alternating tension of the threads.
For this purpose the blade-like material is formed of a smooth spring band bent in the fashion of a cylinder surface and connected to the support element, so that the deflection element forms a bent supporting surface which yields in the direction of the angle bisecting line and is located between the in-running or inbound and the off-running or outbound warp thread sheet and serves for guiding the warp threads which are to be deflected.
This solution is not only expensive, but in order to avoid vibrations at the deflection element it is also necessary to place damping or cushioning, yielding support bodies between the support element and the yielding deflection element. This arrangement makes it difficult to alter the warp thread tension.
From Swiss Pat. No. 596,362 there is known another arrangement, wherein the deflection beam is formed by a light hollow cylinder which is attached to the machine frame by means of pivotal arms and is supported by a pressure cushion extending substantially in the lengthwise direction of the deflection beam. For indication and adjustment of the warp thread tension the pressure cushion is constructed as a substantially hose-like sleeve which is filled with a medium under selectable pressure. This construction is also expensive, in particular with respect to the choice and the retention of the pressure for creating the warp thread tension. With this tensioning apparatus additional supervision or monitoring devices are needed because of the danger of leaks in the pressure cushion.